This species is one of the world's rarest bryophytes. Liverworts vary in appearance, from those with filmy, ribbon-like bodies, to those having leafy structures. Marsh earwort belongs to the latter group, having rounded leaves, and is usually found growing with sphagnum moss. It closely resembles another liverwort, Odontoschisma sphagni.
Liverworts are part of the lower order of the plant kingdom, and are thought to be amongst some of the most ancient of plants surviving on the planet. Bryophytes, as a group, are believed to date back to at least the period called the Devonian, 350-400 million years ago, and possibly even further back to the Silurian. Liverworts, like mosses, do not have conventional roots. They are closely allied to mosses and, indeed, some species resemble mosses and were classified as such until more was known about liverworts in general.
Marsh earwort appears to grow over and amongst Sphagnum mosses in its mire habitat, and seems to prefer level ground. Because of its close resemblance to Odontoschisma, it may have been under-recorded in the past, but a survey in 1996 showed it was present on 96 Sphagnum hummocks at its Argyll site.
This liverwort is now restricted to just three widely separated sites, one in Cornwall, one in Argyll in Scotland, and the third in Craven Arms in Shropshire. However, it was formerly found at other sites in Gloucestershire and Westmorland. Elsewhere, it is known from east Asia, North America and Greenland, although it is considered rare right across its range.
Marsh earwort's main threat is the pollution and enrichment of upland mires and bogs through agricultural run-off, and from the flooding or draining of upland land for reservoir construction. The last three decades have also seen the loss of much of its upland mire habitat due to commercial afforestation.
Marsh earwort is listed as a priority species in the UK Biodiversity Action Plan (UK BAP), and is included in English Nature's Species Recovery Programme. While its Cornish site is protected as a Site of Special Scientific Interest (SSSI), the Argyll site has not, to this date, enjoyed the same legal protection. It is regularly monitored, however, and Scottish Natural Heritage (SNH), who are lead partners for the species within the UK BAP, aim to designate the site as an SSSI or acquire it to be managed as a National Nature Reserve within the next few years.
English Nature, which is monitoring the liverwort at its Cornish site, hopes to investigate the possibilities of re-introducing the plant back to some of its former sites, if they are in a suitable condition. It is also planned to raise the profile of this globally rare species of liverwort elsewhere across its range, in the hope that additional knowledge of the species’ ecology will help with its conservation in the UK.
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